An Octopus that Hears Tornadoes?

A new sensor array was installed in our back yard June 18th. These four instruments are
infrasonic sensors designed to detect acoustic waves from 0.5 to 10 Hz. Similar sensors are installed at the NWS office in Pueblo, CO and at the Boulder Atmospheric Observatory east of Boulder, Colorado. The array is nicknamed "the octopus" since it resembles the sea creature. Each array consists of a central data gathering point with a dozen tentacles that extend about 25 feet in all directions.

Why place fancy listening devices in our back yard? We're helping Dr. Al Bedard, Jr. of the Environmental Technology Laboratory in Boulder, Colorado, determine if the sensor can detect acoustic signatures associated with naturally occurring phenomenon like tornadoes and severe thunderstorms. Recent research indicates that strong, rotating thunderstorms generate low frequency sound waves, and sometimes these sound waves appear tens of minutes before tornado development. These waves occur at frequencies so low (less than 20 Hz) that humans cannot hear them. The "octopus" can, however, detect the low frequency waves, known as infrasonic waves, and alert scientists to that fact.

The display from infrasonic detectors is available to warning meteorologists in the operations area, and data from the display can be quickly compared to radar data to make sure the "octopus" is "hearing" a meteorological phenomenon rather than some other source of infrasound (e.g., rock blasting, rock slides, avalanches).

This is the second appearance of the octopus in our back yard. A prototype infrasonic array was fielded in 2000 as part of the Severe Thunderstorm Electrification and Precipitation Study (STEPS). That sensor caught an infrasonic signature produced by a tornado near Bird City, Kansas.
Questions? E-mail or call the NWS office in Goodland (785-899-7119).

You can also visit the NOAA Environmental Technology Laboratory website at:

If you would like to see more images of the Octopus, Click Here! is the U.S. government's official web portal to all federal, state and local government web resources and services.